1. Field of the Invention
This invention relates to a roof mirror array for use in an optical imaging apparatus.
2. Description of the Prior Art
A roof mirror array comprises a plurality of roof-shaped right angle mirrors disposed in juxtaposed succession, and may be used in an imaging apparatus as disclosed in Japanese Patent Application No. 112,491/1980, for example, filed by the common asignee as the present application. This imaging apparatus comprises a micro-lens array, a micro-roof mirror array disposed rearwardly of the micro-lens array so that the individual lenses and mirrors are in alignment with each other, and a light path splitting right angle mirror of an increased length which is disposed forwardly of the micro-lens array. Light reflected from an object surface is initially reflected by one of the reflecting surfaces of the right angle mirror to pass through the micro-lens for reflection by the micro-roof mirror to be redirected through the micro-lens for the second time and to be projected onto an imaging surface by the other reflecting surface of the right-angle mirror. Such an arrangement provides a compact imaging apparatus having a reduced focal length.
A roof mirror array is generally molded from a plastic material and is formed with a succession of chevron faces having an opening angle of 90.degree. on its front surface, which provides a roof mirror surface. Another succession of chevron faces are formed on the rear surface in a manner such that the peak of one of the front and the rear surface is aligned with the valley of the other surface. A holding frame is disposed in surrounding relationship with the chevron faces on the rear side. The purpose of forming chevron faces on both surfaces is to provide an equal thickness between both of the surfaces in order to prevent the occurrence of shrinkage accompanied by minute pitting during the molding operation. However, while this may prevent a shrinkage and pitting of the roof mirror surface, warpage occurs in a direction perpendicular to the direction of the array as a result of shrinkage during the plastic molding operation, resulting in an opening angle of the individual roof mirror surfaces which is 90.degree.-.DELTA..theta., thus preventing an intended optical response from being obtained. In addition, when mounting the holding frame, if a reference surface of the holding frame is maintained in abutment against a holding member, nonuniform stresses may be applied to the roof mirror surface, causing a distortion thereof or a deviation from the right angle.
Referring to FIGS. 1 to 3, a conventional arrangement will now be described. A conventional roof mirror array 10 comprises a front surface which defines a roof mirror surface formed by a succession of chevron faces 1 having an opening angle of 90.degree., a rear surface formed by another succession of chevron faces 2 or an equal configuration as the chevron faces 1 on the front surface and arranged so that the peak of one of the surfaces is aligned with the valley of the other surface, and a holding frame 3 disposed in surrounding relationship with the exterior of the chevron faces 2 which define the rear surface. The array 1 is integrally formed as by injection molding of a plastics material. The purpose of providing chevron faces on both surfaces of the roof mirror array 10 is to provide an equal thickness between the surfaces so as to prevent a shrinkage accompanied by minute shrinkage during the molding operation. However, while such arrangement effectively prevents a "shrinkage and pitting" of the roof mirror surfaces 1, 2, the shrinkage during the plastics molding operation causes a warpage to occur in the Y-direction which is perpendicular to the array direction X, as shown in FIG. 3, changing the opening angle of the individual roof mirror surfaces to a value 90.degree.-Wr. This prevents an intended optical response from being achieved. In addition, when mounting the molding frame 3, if a reference surface 4 of the frame 3 is held in abutment against a holding member, nonuniform stresses may be applied to the roof mirror surfaces so as to cause a distortion thereof or a deviation from the right angle.